This invention relates to an indicating circuit for an FM stereophonic signal receiver and, in particular, to an indicating circuit capable of providing dual indications of the relative tuning of the receiver and the channel balance thereof.
Tuning indicators are conventionally employed with radio receiving equipment and especially with FM stereophonic signal receivers for enabling an operator to be apprised of the relative tuning condition of the FM receiver with respect to a received FM signal. Such tuning indicators usually are supplied with a DC voltage which is derived from the output of the frequency discriminator included in the FM receiver. Generally, such DC output admits of a magnitude which is a function of the difference between the instantaneous frequency to which the FM receiver is then tuned and the actual frequency of a received signal. The phase, or polarity, of such a DC output indicates whether the FM receiver is then tuned to a higher or lower frequency than the particular frequency of the input signal. In some receivers, the tuning indication is provided by a meter responsive to the magnitude of the aforementioned DC output, irrespective of the polarity thereof. In other receivers, the tuning meter comprises a null meter having a movable pointer that is displaced from a null position in a direction proportional to the polarity of the aforementioned DC output and by an amount which is a function of the magnitude of the DC output. When the receiver is properly tuned to a received signal, the movable pointer is disposed at a center, or null, position.
In stereophonic signal receivers having at least two audio channels (the left and right channels, for example) adjustable controls are provided to permit a listener to selectively adjust the levels of the audio signals transmitted through the respective channels. Generally, preferred sound reproduction is attained when the respective audio signals are balanced with respect to each other. To assist the listener in balancing the audio channels, a suitable indicator, such as a balance meter, is provided. Although such balance meters usually have been incorporated into stereophonic signal amplifiers, it often is preferable to include such meters in stereophonic signal tuners, especially where at least a preliminary balance operation can be performed in the tuner.
It has been found that, if a tuning meter is provided in a stereophonic signal tuner, or signal receiver, and if a balance meter is also provided therein, the attendant cost in providing two independent meters is unnecessarily high. Of course, the tuning meter and/or the balance meter can be of simple contruction to thereby reduce cost. However, such simplification should not be achieved with a resultant loss in accurate indications.